Meeting Abstract
The avian vocal organ, the syrinx, gives rise to highly complex acoustic behavior, and acoustic features of song are thought to be controlled by syringeal musculature. The syringes of suboscines and oscines feature prominent intrinsic syringeal muscles. These groups therefore provide an ideal frame work in which to study the roles of neural control in generating vocal diversity. Oscines, unlike suboscines, exhibit vocal learning, and it is unclear to what degree this difference is reflected in the use of syringeal musculature during song. Previous data from the great kiskadee (Pitangus sulphuratus), a suboscine, suggest syringeal denervation does not appreciably change vocalizations (Amador et al., 2008, J. Neurophysiol., 99(5):2383-9). In this study, we compare the effects of syringeal nerve cuts in western kingbirds (Tyrannus verticalis), a suboscine, and two emberizine oscines (green-tailed towhee, Pipilo chlorurus; fox sparrow, Passerella iliaca), to assess the varying contributions of syringeal control to acoustic properties. Consistent with data from great kiskadees, the frequency of vocalizations of western kingbirds was unaffected by nerve cuts, suggesting syringeal neural control is not required for frequency modulation. In contrast, nerve cuts in both emberizines resulted in a significant reduction of frequency range of the ipsilaterally contributed sounds. The surprising lack of an effect of denervation of syringeal muscles in tyrannids suggests that they modulate frequency by adjusting respiratory pressure, similar to the kiskadee. Thus, syringeal muscles do not contribute to expanding the frequency range of the song repertoire as is seen in oscines (Goller & Riede, 2013, J. Physiol. Paris, 107(3):230-42). Relying on respiratory modulation to adjust frequency severely limits the frequency range of an individual vocal repertoire.
